Open cylindrical rotary drums have been used for many years for the purpose of adding moisture to, or for the drying of, a stream of particulate solid material. Such drums are mounted on rollers with the longitudinal axis inclined from the horizontal so that material passed into the elevated end of the drum will move toward and exit from the lower end. The interior of the drum is usually provided with longitudinal flights attached to the inner surface so that solid materials are lifted as the drum rotates and dropped through the atmosphere within the drum to effect stirring and increased exposure of solid material to the drum atmosphere. For example, in the tobacco industry such drums as used extensively for adding water to tobacco to increase its pliability and reduce breakage during subsequent handling. This is accomplished by mounting water spray nozzles within the drum to spray a mist of water onto the tobacco as it moves through. For this application, there is no need to seal the ends of the drum.
Rotary treating drums are also used for treating tobacco with low quality steam in order to increase the moisture content and temperature of the tobacco. For this application, the ends of the drum are enclosed in a housing in order to prevent the escape of an excessive amount of steam, however, a tight seal is not necessary because escape of a small amount of steam is not detrimental.